Why QA/ QC of Concrete.....

Misconception – Mere Automated and computerized equipment will automatically improve the quality of concrete.

Mere use of sophisticated equipments will not guarantee the desired quality of concrete because:

• RMC is a processed unfinished material at the time of delivery.
• RMC is perishable in its “as sold” condition, will not remain in same plastic condition beyond a limit of time.
• The ultimate quality of concrete (i.e the compressive strength) cannot be verified at the time of supply, it is available only at 28 days from casting.
• The quality of the end product is affected by a variety of factors such as selection of different ingredients, their proportions; variability in the quality of these ingredients and the workmanship employed after the concrete is supplied to the construction site.
• Process control measures required to be taken during production.
• Environmental conditions (ambient temperature, humidity etc.) during transportation and delivery.
• Practices followed during transportation, placement, consolidation and curing/protection of concrete
• High degree of standardization of the products difficult as RMC is compelled to modify and adjust its product to suit locally available materials.
• The product is frequently tested by others – negligence or misinterpretation of standard method of testing.

Material Testing Frequency (as per IS 4926):

Minimum Test Equipments in Laboratory attached to the Plant:

Minimum Specified Laboratory Tests:

• Aggregates:
  • Sampling (IS 2430)
  • Moisture Content (IS 2386 – Part 3)
  • Bulk Density (IS 2386 – Part 3)
  • Sieve Analysis (IS 2386 – Part 1)
• Concrete:
  • Slump (IS 1199)
  • Unit Weight (IS 1199)
  • Compressive Strength (IS 516)

Quality of Incoming Materials:

Control of Final Product:

Optional Test (if specified)

One Sample involves casting of 3 specimens of 150 x 150 x 150 mm size to be tested at 28 days.

Qcrete Concrete Mixes:

• High performance concrete family mixes, most optimized, the mixes are monitored by CUSUM technique as specified in BS EN 206.
• Qcrete does not design concrete mixes as per the examples given in IS 10262.
• Standard mix design methods are useful only for “stand alone” mixes for a particular grade.
• Qcrete adopts “Concrete Family” approach as specified in European Code EN 206.
• Concrete Family: Main Advantages:
  • Changes in concrete quality can be detected rapidly.
  • Action can be taken promptly to ensure production remains in a state of statistical control.,/
  • Reduces assessment period.
• Family of concrete mixes are the mixes that can be reliably relate to each other and are grouped together.
• Combined strength data from the family can be used for conformity control.
• A family of concrete mixes are mix designs of varying proportions for different applications.

CUSUM:

• Qcrete Readymix (India) Pvt. Ltd. uses CUSUM for production control of concrete to meet the quality requirement.
• Qcrete Readymix (India) Pvt. Ltd. is among the few Readymix players in India to implement CUSUM for production control of concrete.
• The CUSUM or cumulative summations measures the performance relative to design intentions.
• The CUSUM system used for monitoring the trends in mean strength (CUSUM M), standard deviation (CUSUM R), and correlationship (CUSUM C) between the early age and 28 days standard strengths.
• The CUSUM assists the detection of the changes in these parameters and suggest action to be taken to ensure the economic concrete production without any strength failure.

When used to monitor concrete strength, the CUSUM system has advantages over other systems:

• The CUSUM system is more sensitive in detecting changes of the magnitude experienced with concrete production.
• Reliable decisions can be made on fewer results.
• The trend of results can be identified from the general slope of a graph.
• The slopes of graphs can be used to determine the magnitudes of properties (ie mean strength and standard deviation).
• Positions of changes in the slopes of graphs indicate approximately when changes occurred.